ALC: issues raised almost 2 month ago + answer from Elecraft

[Enno, PF5X]

Hi gang,
 
Apart from the fundamental discussion "do you really need ALC yes/no", I
have raised this issue already quite some time ago. I have an SPE 1K-FA and
K3 on order, and I want to work both full power barefoot as well as with the
amp, but do not want to run the risk to accidentally overdrive it.  A very
quick response from Wayne gave the following info. Sufficient to cool the
discussion for a while I would say ...
 
-- Enno, PF5X
<quote>

From: wayne burdick [hidden email]

Date: Fri, 12 Oct 2007 14:12:24 -0700

To: [hidden email], [hidden email]

Subject: regarding external ALC

 

Hi Enno,

Transmit power control via the ALC input (AUX I/O pin 15) is planned, but
not finalized. We're mindful of the negative impact ALC can have on transmit
signal purity, a subject of recent debate within testing organizations.

External amplifiers vary widely in their loop gain, causing problems with
distortion. Many amplifiers, like the Alpha 87a, specifically say not to use
external ALC. A properly operating, internally ALC controlled rig like the
K3 does not need external ALC input to connect to an external amp. In
general, external ALC should -not- be used as a way to control rig power.

As for the voltage range, this is not a typo: the ALC input handles 0 to +5
V. Once ALC is working to our satisfaction, we'll provide simple interfacing
information that will allow the use of negative control voltages (probably a
resistive divider pulled up to a positive supply, or at most an op-amp
circuit).

Meanwhile, the K3's DSP-based early-stage ALC is very effective at
preventing amplifier overdrive, and should suffice in nearly all cases.

73,

Wayne

N6KR

<unquote>
 
 
 
 

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[Jerry Flanders]

At 02:59 PM 12/3/2007, Enno, PF5X wrote:
>Hi gang,
>
><SNIP> A very
>quick response from Wayne gave the following info. Sufficient to cool the
>discussion for a while I would say ...
>

Not so - Wayne's comments seem directed at those who might want to
use ALC as if it were a substitute for the mike gain control.

It worries me when I see the discussion wander away from amplifier
safety in an antenna catastrophe situation, which is my main concern.
I once blew up the output circuit of an AL1200 due to an intermittent
in an antenna coax while running full power on RTTY.

Please see my other in-line comments below.

>--
><quote>
>
>From: wayne burdick [hidden email]
>
>Date: Fri, 12 Oct 2007 14:12:24 -0700
>
>To: [hidden email], [hidden email]
>
>Subject: regarding external ALC
>
>
>
>Hi Enno,
>
>Transmit power control via the ALC input (AUX I/O pin 15) is planned, but
>not finalized. We're mindful of the negative impact ALC can have on transmit
>signal purity, a subject of recent debate within testing organizations.

Speaking only for myself, I do not intend to adjust the ALC to
provide normal level control - only a crisis shutdown function.
Quoting from my Quadra's manual p4.:

"The ALC cable must be connected between
the transceiver and VL-1000 to
prevent overdrive of the amplifier, and especially
to facilitate the proper operation of the
protection circuitry if sudden antenna system
problems should cause the SWR to rise to dangerous
levels."

Rightly or wrongly, Yaesu (and probably ICOM) engineers have presumed
the ALC would be functional and could cut back exciter drive in the
event of an antenna catastrophe. Other main-line rigs that I am
familiar with are compatible. I think it is reasonable to assume the
world-class K3 would have provided for this also.

BTW - It is worrisome that ALC was only planned, but still not
finalized, as of Oct 12.

<snip>
>  Once ALC is working to our satisfaction, we'll provide simple interfacing
>information that will allow the use of negative control voltages ...

I, and perhaps other Solid State amp users, would prefer a definite
calendar commitment, if that is possible. If not possible, please
state so. I would hope for a working, properly engineered
negative-going ALC fix within a few months.

>Meanwhile, the K3's DSP-based early-stage ALC is very effective at
>preventing amplifier overdrive, and should suffice in nearly all cases.

I repeat -  my concern is amplifier safety, not a substitute for a
mike gain control. Sooner or later, the antenna will fail, but we
don't know when,  and we probably cannot manually cut back drive
quickly enough to protect those expensive SS finals when it occurs.

>73,
>
>Wayne
>
>N6KR


Jerry W4UK


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[Don Wilhelm-4]

Jerry and all,

OTOH, I would be quite uncomfortable purchasing a modern SS amplifier
that did not implement protection from excessive SWR without depending
on the exciter to throttle back the power.

To my mind, depending on some external device (the exciter) to protect
the amp is a recipe for failure and represents faulty design decisions
from the amplifier designers.

73,
Don W3FPR

Jerry Flanders wrote:
>
> I repeat -  my concern is amplifier safety, not a substitute for a
> mike gain control. Sooner or later, the antenna will fail, but we
> don't know when,  and we probably cannot manually cut back drive
> quickly enough to protect those expensive SS finals when it occurs.
>
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[Vic K2VCO]

Jerry Flanders wrote:

> Not so - Wayne's comments seem directed at those who might want to use
> ALC as if it were a substitute for the mike gain control.
>
> It worries me when I see the discussion wander away from amplifier
> safety in an antenna catastrophe situation, which is my main concern. I
> once blew up the output circuit of an AL1200 due to an intermittent in
> an antenna coax while running full power on RTTY.

Although ALC can be used for amplifier protection, it's the worst way to
do it, because it depends on things not in the control of the amp
designer. A well-designed amplifier should be able to protect *itself*
from high reflected power, overdrive, etc. by taking itself offline.

> "The ALC cable must be connected between
> the transceiver and VL-1000 to
> prevent overdrive of the amplifier, and especially
> to facilitate the proper operation of the
> protection circuitry if sudden antenna system
> problems should cause the SWR to rise to dangerous
> levels."

This is exactly now NOT to do it. How do you know you have the system
adjusted properly? The *only* way you could depend on this is with an
amplifier and transceiver of the same manufacture, specifically designed
to work together. Suppose you were driving it with an ICOM transceiver
and it blew up? Would you complain to Yaesu because the amp failed to
raise ALC quickly enough or to ICOM because the transceiver didn't
respond in time?

> I, and perhaps other Solid State amp users, would prefer a definite
> calendar commitment, if that is possible. If not possible, please state
> so. I would hope for a working, properly engineered negative-going ALC
> fix within a few months.

How will you know it's 'properly engineered'? They are not going to
guarantee that your brand-x amplifier won't blow up!

Of course, you do have the option of waiting for it to become available
before purchasing a K3. I wrote Bill Gates and demanded a calendar
commitment for Vista to support 'standard' HLP files. He didn't answer!

I still don't know how you would verify that it actually provides the
protection that you want.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[dave.wilburn]

I admit, I may not be the sharpest knife in the drawer, but to see a
reference to an amp, and the words 'full power' and RTTY, all together?
Wow.  That raised my eyebrows.  

With the power density of RTTY, isn't that a full blown stress test of
your complete RF system, at 100% duty cycle, or so...?  Any standing
waves on the thing would be huge, and wouldn't the safety factor would
be a negative number?

Aren't you taking on a bit of risk to your system?  Please don't take
the wrong way, I am trying to learn.  Being one of those no-code techs
we hear so much about.  I am just rationalizing the described activity,
with all these warnings I see on various equipment, about high duty
cycle modes.
-  

David Wilburn
[hidden email]
K4DGW
K2 S/N 5982


On Mon, 2007-12-03 at 16:43 -0500, Jerry Flanders wrote:

> At 02:59 PM 12/3/2007, Enno, PF5X wrote:
> >Hi gang,
> >
> ><SNIP> A very
> >quick response from Wayne gave the following info. Sufficient to cool the
> >discussion for a while I would say ...
> >
>
> Not so - Wayne's comments seem directed at those who might want to
> use ALC as if it were a substitute for the mike gain control.
>
> It worries me when I see the discussion wander away from amplifier
> safety in an antenna catastrophe situation, which is my main concern.
> I once blew up the output circuit of an AL1200 due to an intermittent
> in an antenna coax while running full power on RTTY.
>
> Please see my other in-line comments below.
>
> >--
> ><quote>
> >
> >From: wayne burdick [hidden email]
> >
> >Date: Fri, 12 Oct 2007 14:12:24 -0700
> >
> >To: [hidden email], [hidden email]
> >
> >Subject: regarding external ALC
> >
> >
> >
> >Hi Enno,
> >
> >Transmit power control via the ALC input (AUX I/O pin 15) is planned, but
> >not finalized. We're mindful of the negative impact ALC can have on transmit
> >signal purity, a subject of recent debate within testing organizations.
>
> Speaking only for myself, I do not intend to adjust the ALC to
> provide normal level control - only a crisis shutdown function.
> Quoting from my Quadra's manual p4.:
>
> "The ALC cable must be connected between
> the transceiver and VL-1000 to
> prevent overdrive of the amplifier, and especially
> to facilitate the proper operation of the
> protection circuitry if sudden antenna system
> problems should cause the SWR to rise to dangerous
> levels."
>
> Rightly or wrongly, Yaesu (and probably ICOM) engineers have presumed
> the ALC would be functional and could cut back exciter drive in the
> event of an antenna catastrophe. Other main-line rigs that I am
> familiar with are compatible. I think it is reasonable to assume the
> world-class K3 would have provided for this also.
>
> BTW - It is worrisome that ALC was only planned, but still not
> finalized, as of Oct 12.
>
> <snip>
> >  Once ALC is working to our satisfaction, we'll provide simple interfacing
> >information that will allow the use of negative control voltages ...
>
> I, and perhaps other Solid State amp users, would prefer a definite
> calendar commitment, if that is possible. If not possible, please
> state so. I would hope for a working, properly engineered
> negative-going ALC fix within a few months.
>
> >Meanwhile, the K3's DSP-based early-stage ALC is very effective at
> >preventing amplifier overdrive, and should suffice in nearly all cases.
>
> I repeat -  my concern is amplifier safety, not a substitute for a
> mike gain control. Sooner or later, the antenna will fail, but we
> don't know when,  and we probably cannot manually cut back drive
> quickly enough to protect those expensive SS finals when it occurs.
>
> >73,
> >
> >Wayne
> >
> >N6KR
>
>
> Jerry W4UK
>
>
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[David Cutter]

In my view there are 2 issues here:

1   in my view the amplifier should be self-protecting against overloads, eg
antenna fault (I am mindful of virtually any other equipment which must be
tested by law with overload conditions)

2   ALC has its problems and thus not always connected, but everyone uses
PTT which can be very easily disabled (allow the rig to self protect) or tx
inhibit, tx enable, or others?

ALC is an analog signal for gradually reducing drive, which might not be
appropriate for shutdown.

David
G3UNA

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[Jerry Flanders]

At 05:03 PM 12/3/2007, Don Wilhelm wrote:
>Jerry and all,
>
>OTOH, I would be quite uncomfortable purchasing a modern SS
>amplifier that did not implement protection from excessive SWR
>without depending on the exciter to throttle back the power.

Good point. I think I would prefer this also. But I already have two
Quadras in a SO2R station. Had them for years. Presently both are
driven by ICOM rigs, and I was hoping for an easy changeover to two
K3s without raising new amp safety issues.

I think if I were starting completely from scratch, I might go with
amps that are totally self-protected if they are completely automatic
as are these Quadras. Quadra automation is superb.

>To my mind, depending on some external device (the exciter) to
>protect the amp is a recipe for failure and represents faulty design
>decisions from the amplifier designers.
>
>73,
>Don W3FPR

Maybe, but the Quadra has been a mainline successful product now for
around ten years. Yaesu engineers probably know what they are doing.
But maybe they made decisions strictly for their internal product
line just as, perhaps, Elecraft may now be doing(?).

Jerry W4UK

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[Geoffrey Mackenzie-Kennedy]

 David Cutter <[hidden email]> wrote
on Monday, December 03, 2007 10:55 PM :


> In my view there are 2 issues here:
>
> 1   in my view the amplifier should be self-protecting against overloads,
> eg antenna fault (I am mindful of virtually any other equipment which must
> be tested by law with overload conditions)

Without question! I believe that a shutdown system of any use should
shutdown the entire transmitter not just the amplifier, and start the
cooling fans if not already running.

73,
Geoff
GM4ESD






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[Joe Subich, W4TV]

> 2   ALC has its problems and thus not always connected, but
> everyone uses PTT which can be very easily disabled (allow
> the rig to self protect) or tx inhibit, tx enable, or others?

I STRONGLY disagree ... I WANT a graceful foldback if the antenna
SWR is slightly out of range.  10% reflected power should not take
an amplifier off line.  However there should be some way to cause
the exciter to reduce its power output so the amplifier does not
generate voltages or currents that will cause the demise of the
active devices.  

Unless one has an amplifier and exciter that share a common
control microprocessor with data feedback or the amplifier has
an extremely sophisticated and FAST attenuator in the drive
line, ALC (e.g., an external gain control) is the appropriate
means of reducing power gradually.  

Sure, if the reflected power is so high that it indicates an
antenna failure (50% reflected power), the appropriate action
is to disable the amplifier and potentially even the exciter
but that's over the top for 10% reflected power (2:1 SWR) or
even 20% reflected power (3:1 SWR).

73,

   ... Joe, W4TV
   

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of David Cutter
> Sent: Monday, December 03, 2007 5:55 PM
> To: Elecraft Reflector
> Subject: [Elecraft] linear amp shutdown (was ALC)
>
>
> In my view there are 2 issues here:
>
> 1   in my view the amplifier should be self-protecting
> against overloads, eg
> antenna fault (I am mindful of virtually any other equipment
> which must be
> tested by law with overload conditions)
>
> 2   ALC has its problems and thus not always connected, but
> everyone uses
> PTT which can be very easily disabled (allow the rig to self
> protect) or tx
> inhibit, tx enable, or others?
>
> ALC is an analog signal for gradually reducing drive, which
> might not be
> appropriate for shutdown.
>
> David
> G3UNA
>

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[Joe-aa4nn]

Right on, Don.
The amp must protect itself by itself and for itself.
Like Overdrive, High SWR, Hi drain current, ad infinitum.
Modern SS amplifiers all have this built in protection.
Like many, I have never used ALC, being CW only, but I
take care of drive power to protect the amplifier.
de Joe, aa4nn

-----Original Message-----
>From: Don Wilhelm <[hidden email]>
>OTOH, I would be quite uncomfortable purchasing a modern SS amplifier
>that did not implement protection from excessive SWR without depending
>on the exciter to throttle back the power.
>
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[David Cutter]

Joe

I take your point entirely which is why I said

"ALC is an analog signal for gradually reducing drive, which
 might not be appropriate for shutdown."

Shutdown for me is for protection against gross overload and for this
another signal might be more appropriate.  Since many users do not connect
ALC, some other signal for protection should/could be provided.  The problem
yet again is that users might still ignore what the manufacturer offers, so,
the amplifier must protect itself.

 David
G3UNA

----- Original Message -----
From: "Joe Subich, W4TV" <[hidden email]>
To: "'David Cutter'" <[hidden email]>; "'Elecraft Reflector'"
<[hidden email]>
Sent: Tuesday, December 04, 2007 2:03 AM
Subject: RE: [Elecraft] linear amp shutdown (was ALC)

>
>> 2   ALC has its problems and thus not always connected, but
>> everyone uses PTT which can be very easily disabled (allow
>> the rig to self protect) or tx inhibit, tx enable, or others?
>
> I STRONGLY disagree ... I WANT a graceful foldback if the antenna
> SWR is slightly out of range.  10% reflected power should not take
> an amplifier off line.  However there should be some way to cause
> the exciter to reduce its power output so the amplifier does not
> generate voltages or currents that will cause the demise of the
> active devices.
>
> Unless one has an amplifier and exciter that share a common
> control microprocessor with data feedback or the amplifier has
> an extremely sophisticated and FAST attenuator in the drive
> line, ALC (e.g., an external gain control) is the appropriate
> means of reducing power gradually.
>
> Sure, if the reflected power is so high that it indicates an
> antenna failure (50% reflected power), the appropriate action
> is to disable the amplifier and potentially even the exciter
> but that's over the top for 10% reflected power (2:1 SWR) or
> even 20% reflected power (3:1 SWR).
>
> 73,
>
>   ... Joe, W4TV
>
>
>
>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of David Cutter
>> Sent: Monday, December 03, 2007 5:55 PM
>> To: Elecraft Reflector
>> Subject: [Elecraft] linear amp shutdown (was ALC)
>>
>>
>> In my view there are 2 issues here:
>>
>> 1   in my view the amplifier should be self-protecting
>> against overloads, eg
>> antenna fault (I am mindful of virtually any other equipment
>> which must be
>> tested by law with overload conditions)
>>
>> 2   ALC has its problems and thus not always connected, but
>> everyone uses
>> PTT which can be very easily disabled (allow the rig to self
>> protect) or tx
>> inhibit, tx enable, or others?
>>
>> ALC is an analog signal for gradually reducing drive, which
>> might not be
>> appropriate for shutdown.
>>
>> David
>> G3UNA
>>
>

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[Geoffrey Mackenzie-Kennedy]

 From: David Cutter G3UNA

> I take your point entirely which is why I said
>
> "ALC is an analog signal for gradually reducing drive, which
> might not be appropriate for shutdown."
>
> Shutdown for me is for protection against gross overload and for this
> another signal might be more appropriate.  Since many users do not connect
> ALC, some other signal for protection should/could be provided.  The
> problem yet again is that users might still ignore what the manufacturer
> offers, so, the amplifier must protect itself.

-------------------------------------------------------------------

David,

It has always been my understanding that normal and good practice is for a
shutdown system to actually *shutdown* the entire transmitter affected in
the event of gross overload / failure, e.g. *abnormal* VSWR, cooling system
failure etc.  A system which protects the amplifier only could still result
in damage to the exciter / driver under some circumstances of gross overload
/ failure, for example when using my K2/100 a while back during some contest
wind toppled a large pine across the antenna in use, the KAT100 sparkled and
both the KPA100 and K2 were damaged. My K2/100 is now protected by the total
shutdown system used with my other rigs, something that I should have done
before ever using the K2/100 at this location.

I take your point that the amplifier should be able to protect itself  if
people ignore what is offered.

73,
Geoff
GM4ESD

 .




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[David Cutter]

Geoff

With so many combinations of rig and amplifier a 'standard' would be good,
(the Collins ALC started it all I understand) but in its absence each
operator needs to make provision for their own station protection.

With the advent of solid state amplifiers there was a chance to make a new
standard to help us all, perhaps someone knows if this was taken up .  It
would be good to know how folks have covered themselves with various
rig/amplifier combinations and  I wonder how the Elecraft linears will do
this.  I see the SPE linear has 3 stages of protection for instance: SIMPLE
= audible alarm, SERIOUS = switch to standby and FATAL = complete shutdown,
but these do not shutdown the driving transmitter as far as I can see.
After all, running barefoot is better than nothing in a contest, so,
shutting down the transmitter is not always desirable.

David
G3UNA


----- Original Message -----
From: "Geoffrey Mackenzie-Kennedy" <[hidden email]>
To: "David Cutter" <[hidden email]>
Cc: "Elecraft Discussion List" <[hidden email]>
Sent: Tuesday, December 04, 2007 12:46 PM
Subject: Re: [Elecraft] linear amp shutdown (was ALC)

> From: David Cutter G3UNA
>
>> I take your point entirely which is why I said
>>
>> "ALC is an analog signal for gradually reducing drive, which
>> might not be appropriate for shutdown."
>>
>> Shutdown for me is for protection against gross overload and for this
>> another signal might be more appropriate.  Since many users do not
>> connect ALC, some other signal for protection should/could be provided.
>> The problem yet again is that users might still ignore what the
>> manufacturer offers, so, the amplifier must protect itself.
>
> -------------------------------------------------------------------
>
> David,
>
> It has always been my understanding that normal and good practice is for a
> shutdown system to actually *shutdown* the entire transmitter affected in
> the event of gross overload / failure, e.g. *abnormal* VSWR, cooling
> system failure etc.  A system which protects the amplifier only could
> still result in damage to the exciter / driver under some circumstances of
> gross overload / failure, for example when using my K2/100 a while back
> during some contest wind toppled a large pine across the antenna in use,
> the KAT100 sparkled and both the KPA100 and K2 were damaged. My K2/100 is
> now protected by the total shutdown system used with my other rigs,
> something that I should have done before ever using the K2/100 at this
> location.
>
> I take your point that the amplifier should be able to protect itself  if
> people ignore what is offered.
>
> 73,
> Geoff
> GM4ESD
>
> .
>
>
>
>

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[N2TK]

David,
I hope when Elecraft comes out with their amp that it has features like my
Acom 2000A - if there is an arc, high swr or overdriven the amp shuts down
quickly without damage to it. When this happens I can quickly check to see
if I am on the wrong antenna, too much drive or a problem with an
antenna/feedline. When this happens I am still able to run barefoot.

With most of my rigs over the years I have used a power mosfet to key the
amp. With the Kenwoods and Icoms I have bypassed their amp keying relay to
pick up a quicker transmit-on signal from the rig. This way I have a better
chance of the amp's relay pulled in before RF gets to the amp. Some rigs put
out an RF spike at key-down. This causes the amp to kick out. None of the
rigs I have had so far have had this problem. I don't use the mosfet keying
with my K2 since it really doesn't have fast QSK. Hopefully the K3 will have
QSK as good as the TS-930 and TS-940.

73,
N2TK, Tony

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of David Cutter
Sent: Tuesday, December 04, 2007 8:33 AM
To: Geoffrey Mackenzie-Kennedy
Cc: Elecraft Discussion List
Subject: Re: [Elecraft] linear amp shutdown (was ALC)

Geoff

With so many combinations of rig and amplifier a 'standard' would be good,
(the Collins ALC started it all I understand) but in its absence each
operator needs to make provision for their own station protection.

With the advent of solid state amplifiers there was a chance to make a new
standard to help us all, perhaps someone knows if this was taken up .  It
would be good to know how folks have covered themselves with various
rig/amplifier combinations and  I wonder how the Elecraft linears will do
this.  I see the SPE linear has 3 stages of protection for instance: SIMPLE
= audible alarm, SERIOUS = switch to standby and FATAL = complete shutdown,
but these do not shutdown the driving transmitter as far as I can see.
After all, running barefoot is better than nothing in a contest, so,
shutting down the transmitter is not always desirable.

David
G3UNA




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